Armour panels

ABSTRACT

Described herein are armour panels that can be used to protect entities such as vehicles, buildings or organisms from overpressure either in the form of an explosion (shockwave) or projectile (bullet, shrapnel etc). In particular, the invention relates to the use of a combination of layers to form a panel with pressure impulse mitigating properties to provide an armour panel which is lightweight, cheap to manufacture and yet strong enough to withstand impact from high velocity ballistics, fragments and the like.

This invention relates to armour panels which can be used to protect entities such as vehicles, buildings or organisms from overpressure either in the form of an explosion (shockwave) or projectile (bullet, shrapnel etc). In particular, the invention relates to the use of a combination of layers to form a panel with pressure impulse mitigating properties to provide an armour panel which is lightweight, cheap to manufacture and yet strong enough to withstand impact from high velocity ballistics, fragments and the like.

BACKGROUND

Increased levels of insurgent related warfare have led to the need to protect vehicles and/or personnel from munitions typically used in this type of warfare, such as small arms fire and improvised explosive devices (LEDs). While a variety of means are available to minimize casualties from these threats, the use of suitable armour remains an important last line of defence. As a result of the need to protect a large number of potential targets while not hindering their mobility, it is also important to be able to provide armour that is lightweight and relatively inexpensive. Armour piercing (AP) ammunition is designed to penetrate the hardened armour of modern military vehicles. It typically includes a sharp, hardened steel or tungsten carbide penetrator covered with a metal jacket that adds mass and allows the projectile to conform to a rifled barrel and spin for accuracy. When an AP round hits armour, the guilding is rapidly deformed and drops away, leaving the sharpened penetrator travelling with a high velocity to bore its way through the armour.

The use of composite armours based on glass fibres is known. Studies indicate that sharp-nosed projectiles tend to move the fibres within a composite armour panel laterally away from the advancing projectile, resulting in kinked fibres around the penetration cavities but with little energy absorption. Thus, the primary reason why armour-piercing projectiles are so effective against fibre-based composite armour is that neither the fibre nor matrix material of the composite is hard enough to cause deformation of the sharp, hardened penetrator nose.

Ceramic based armour systems have therefore been developed to defeat AP ammunition. These break up the projectile in the ceramic material and terminate the fragment energy in a backing plate that supports the ceramic. Such systems often suffer however from unacceptable damage after projectile impact. Their ability to defeat subsequent impacts is seriously reduced.

In U.S. Pat. No. 7866248, a composite armour is taught that includes a disruptive layer including a sheet of adjoining polygonal ceramic tiles encased by a retaining polymer, the ceramic tiles having a non-spherical deflecting front surface, and a backing layer adjacent to the disruptive layer.

The present inventors have realised that it is highly advantageous to break, blunt or otherwise redirect the tip of a ballistic penetrator. This reduces its penetrative efficiency by orders of magnitude. A blunt or broken penetrator, or one that has been tipped off axis even slightly will find it much harder to penetrate subsequent layers of an armour material because it cannot generate as much pressure at a given point.

This reduces or stops its ability to cause a catastrophic failure and immediately pierce an armour. In a multilayer system, this means that the penetrator has to push the subsequent layers ahead of it, which in turn requires that it rip the entire layer aware from its entire contact surface area across the entire panel.

The present inventors therefore seek to induce this blunting, breaking, or stumbling process and provide a strong yet lightweight and cheap armour. The inventors envisage the use of disruptor particles in order to effect this process.

In order to provide an armour panel with sufficient strength, this can be achieved in conjunction with a separate ceramic plate that can be used pre or post the disruptor particle layer. These are preferably small spheres of strong material such as ceramics which can be used to deflect an incoming penetrator.

The use of disruptor particles in armour is, however, not new. In WO2006/125969, pressure impulse mitigating barriers comprising a water gel layer, e.g. a cross-linked water gel layer, and a layer comprising a plurality of disruptor particles, e.g. a layer of ceramic spheres are mentioned.

The present inventors sought however to improve upon the general principles set out in that document. In particular, the inventors sought to improve performance over the materials of WO2006/125969.

The present invention relies on the use of both a layer of disruptor particles preferably set in an adhesive such as an epoxy resin in combination with a ceramic tile layer to further blunt penetrator force. In still more preferred embodiments multiple panels of the invention can be used, separated by a gap, to still further enhance performance. The resulting panels are lightweight and are capable of outperforming equivalent weights of more conventional armouring. Their utility therefore in military and civilian applications is widespread. The panels of the invention are relatively low cost and meet military standards for ballistics protection.

SUMMARY OF INVENTION

Viewed from one aspect the invention provides a composite armour comprising:

(I) a ceramic tile layer;

(II) a disruptor particle layer embedded within an adhesive; and

(III) a backing layer.

Viewed from another aspect the invention provides a composite armour comprising at least two armour panels, each panel independently comprising:

(I) a ceramic tile layer;

(II) a disruptor particle layer embedded within a hydrogel or an adhesive;

(III) a backing layer;

said panels being separated from each other by a gap, such as an air gap e.g. of 5 to 200 mm.

Viewed from another aspect the invention provides a composite armour comprising at least two armour panels, each panel independently comprising:

(I) a disruptor particle layer embedded within a hydrogel or an adhesive;

(II) a backing layer;

said panels being separated from each other by a gap, e.g. of 5 to 200 mm.

Viewed from another aspect the invention provides the use of a composite armour as hereinbefore described to protect an entity from pressure impulse, e.g. a bullet.

Viewed from another aspect the invention provides an entity such as a vehicle, helmet or body armour comprising a composite armour as hereinbefore defined.

Viewed from another aspect the invention provides an object such as a vehicle being adapted to carry a composite armour comprising:

(I) a disruptor particle layer embedded within a hydrogel or an adhesive;

(II) a backing layer;

wherein said composite armour is removably attached to the object.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

FIG. 1 shows a non-exemplary method for producing the panels described herein.

FIGS. 2A and 2B show the aim and actual hit points, respectively, on the panel.

FIGS. 3A-3C show the reconstruction of the probable FSP/panel interactions until the impact with the second panel.

DEFINITIONS

The terms outer and inner are used herein to dictate the relative positions of layers relative to an incoming pressure impulse such as a projectile. An outer layer will therefore be struck by a projectile before an inner layer. These terms do not negate the possibility that there are other more “outer” or more “inner” layers or layers between the inner and outer layers in question.

The term pressure impulse mitigation covers mitigating the effects of contact with a projectile, i.e. mitigating the potential damage caused by a projectile or in the mitigation of projectile induced damage. The projectile may be, for example, a bullet, missile, shrapnel, etc. A pressure impulse mitigating barrier is therefore capable of mitigating these effects.

By entity is meant anything which should be protected from the impact of an explosion or from damage by a projectile, e.g. structures, organisms and the general physical environment.

An organism is a living plant or animal, e.g. a human. By structure is meant any inanimate object which could be protected from explosive damage such as buildings (temporary or permanent), industrial plant, civil infrastructure, vehicles, military equipment, computers etc.

The term removeably attached means that the panel can be attached to an entity and taken off again when desired.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relies on the concept that if a penetrator encounters a sphere (or similar shaped disruptor particle), it will deflect off the side of that particle before it crushes the particle. By deflecting an incoming penetrator, it can induce yaw or a less than optimal spin, or cause the penetrator to be blunted. This makes the projectile easier to stop. The present invention therefore primarily relates to stopping a spinning bullet of any calibre, e.g. from small arms fire through to much larger calibres associated with automatic weaponry such as an M2 rifle.

The present inventors have realised however, that a layer of disruptor particles on its own is insufficient to defeat these high calibre weapons and they therefore propose the combination of disruptor particles and a ceramic tile. The ceramic tile, whether inner or outer to the disruptor particle layer, serves to further blunt the impact from the projectile.

The invention also employs a backing layer, e.g. of cross-linked polymer to provide the strength needed to stop projectiles.

Ceramic Tile Layer

The armour panels of the invention preferably comprise a continuous ceramic tile layer. The word continuous is used here to distinguish the disruptor particle layer which might be ceramic but is not continuous. The ceramic tile layer is formed from one or more ceramic tiles which are arranged to as to form an essentially continuous sheet of ceramic across the armour panel. The materials which can be used in such a ceramic tile are the same as those which can be used to make disruptor particles discussed below.

Examples of ceramic materials that are suitable for use in forming ceramic tiles are aluminium oxide, zirconia toughened alumina, precipitation strengthened alumina, magnesium oxide, SiAlON (Silicon oxy-nitride), silicon carbide, silicon nitride, silicon oxide, boron carbide, aluminium borides, boron nitride, titanium diboride or more generally from a group of oxides, boride, carbides, nitrides of alkaline earth, Group IIA, IIIB, IVB and transition metals and mixtures thereof.

In addition, a metal matrix composite containing a ceramic phase is also suitable. The use of carbides and in particular SiC is especially preferred.

The density of the ceramic is an important factor in determining its strength. For example, alumina ceramic material is formed into ceramic tiles that have a density greater than 3.5 g/cubic centimeter (cc), with density ranging from 3.8 g/cc to 3.97 g/cc (or between 95 and 99.9% of theoretical density) being preferred. Other ceramic materials' densities are even lower than that of alumina. For instance, relatively pure (>99%) SiC has a density of about 3.2 g/cc and boron carbide has density even lower than that of SiC which is about 2.8 g/cc. The ceramic density may be in the range of 1.5 to 5 g/cc.

Ceramic tiles having areal density ranging from about 10 to 25 kg/m² are preferred. Suitable ceramic tiles can be prepared according to methods known to those skilled in the art, such as by compression moulding and sintering or hot pressing. The nature of the specific threat will determine a range of areal densities needed for a particular type of armour.

By adopting the strategy of deflection using a disruptor particle layer described below areal densities of the armour of the invention can be significantly lower (<50%) than that of rolled homogenous armour (RHA) needed to defeat identical threat level.

Tile dimensions can vary. It can be considered that the more joints there are in a tile layer, the more areas of potential weakness however, the presence of j oints prevents crack propagation in a tile layer once impact occurs. It is preferred therefore to use a plurality of tiles to make up the tile layer as a whole and not just a large single tile. Tiles can be 5 to 20 cm in either dimension.

Tiles preferably are 3 to 20 mm in thickness, preferably 4 to 10 mm in thickness. It will be appreciated that thicker tiles tend to mean stronger tiles but extra weight. The idea here is to maximise strength whilst minimising weight. The dimensions above are a compromise therefore between strength and weight.

Disruptor Particle Layer

The armour panel of the invention comprises at least one layer comprising a plurality of disruptor particles. By disruptor particles is meant irregular or preferably regular shaped particles, e.g. spheres of material. The disruptor particle layer is preferably embedded within an adhesive such as an epoxy resin or embedded within a hydrogel.

It has been surprisingly found that an adhesive such as an epoxy layer in combination with a disruptor particle layer gives rise to still further improvements in pressure impulse mitigation.

The disruptor particles may be formed from a wide variety of materials such as fibreglass, graphite, stone (sandstone, quartz, basalt, flint, pumice), metals (steel), glass (e.g. hollow spheres of glass), polymers (e.g. polyethylene) but are preferably ceramic particles.

By ceramic is meant inorganic non-metallic material such as alumina, beryllia, steatite or sterite, whose final characteristics are produced by subjection to high temperatures, e.g. in a kiln. Often the ceramic material derives from clay. Preferred ceramic materials are aluminium oxide, zirconia toughened alumina, precipitation strengthened alumina, magnesium oxide, SiAlON (Silicon oxy-nitride), silicon carbide, silicon nitride, silicon oxide, boron carbide, aluminium borides, boron nitride, titanium diboride or more generally from a group of oxides, boride, carbides, nitrides of alkaline earth, Group IIA, IIIB, IVB and transition metals and mixtures thereof.

In addition, metal matrix composite containing ceramic phase are also suitable. The use of carbides and in particular SiC is especially preferred. One of the other benefits of the disruptor layer is that it might deliver the same performance/threat defeat at not only same/less areal density, but might also be so effective as to permit the use of cheaper, low grade ceramics. It would be a major benefit to use alumina in armour systems rather much more expensive carbides.

Ceramic particles of use in the invention may be manufactured as is known in the art from materials discussed above although preferably these are formed from aluminium oxide, silicon carbide or silicon nitride. Aluminium oxide ceramic particles may be at least 98%, e.g. at least 99% alumina and may have a Vickers hardness of at least 1300, e.g. at least 1700 Hv. They may also have a modulus of elasticity of 300 to 400 kNmm⁻², e.g. 350 kNmm⁻², a fracture toughness of 10 to 20 MPam⁻², e.g. 13.5 MPam⁻² and an ultimate compressive strength of 1 to 5 kNmm⁻², e.g. 2.5 kNmm⁻².

Silicon nitride ceramic balls (Si₃N₄), may comprise between 80 and 90%, e.g. 87% silicon nitride and may have a Vickers hardness of at least 1300, e.g. at least 1400 Hv, such as 1400 to 1700 Hv. They may also have a modulus of elasticity of 250 to 400 kNmm⁻², e.g. 310 kNmm⁻², a fracture toughness of 4 to 10 MPam⁻², e.g. 6 to 8 MPam⁻² and an ultimate compressive strength of 2 to 7 kNmm⁻², e.g. 4 kNmm⁻².

The use of Silicon carbide is especially preferred. Silicon carbide ceramic balls (SiC), may comprise between 80 and 90%, silicon carbide and may have a Vickers hardness of at least 1300, e.g. at least 1400 Hv, such as 1400 to 1700 Hv. They may also have a modulus of elasticity of 250 to 400 kNmm⁻², e.g 310 kNmm⁻², a fracture toughness of 4 to 10 MPam⁻², e.g. 6 to 8 MPam⁻² and an ultimate compressive strength of 2 to 7 kNmm⁻², e.g. 4 kNmm⁻².

All the ceramics of use in the invention, whether part of a particle or tile are inert, non-toxic and essentially unaffected by heat (they will function at temperatures of greater than 1000° C.) making them ideal for use in the barriers of the invention. Ceramics also weigh considerably less than steel, typically 50% less. Thus for example, aluminium oxide ceramics have a density of approximately 3.8 to 3.9 g/cm³, and silicon nitride ceramics a density of around 3.2 to 3.25 g/cm³. In contrast steel has a density of the order of 7.8 g/cm³. The use of ceramic disruptor particles as opposed to steel particles is therefore of significant benefit in terms of barrier weight. Thus, a barrier with the same performance as steel can be prepared using the panels of the invention at much lower weight.

Moreover, the Vickers hardness index of steel is around 700 to 800 Hv and is therefore approximately 50% less than that of the ceramics discussed above. The size of the disruptor particles may vary over a broad range. Preferred diameters range from 0.1 mm to 20 mm, preferably 0.5 to 10 mm, e.g. 1 to 5 mm. It may also be possible to use particularly small disruptor particles of the order of 10 to 1000 microns in diameter. Such miniature particles are generally hollow ceramic spheres (e.g. formed of sodium borosilicate). Preferred ceramic spheres are solid. It will be appreciated that all the particles should be of approximately the same size in order to allow easy packing. Thus particle size distribution should preferably be narrow, e.g. all particles should have diameters within 10% of the mean, preferably within 5% of the mean.

Preferably the disruptor particles are regularly shaped so that they pack using a minimum amount of space. Suitable shapes therefore include cubes and cuboids, a honeycomb type structure or spherical structures, e.g. ovoid or spheres. The particles are preferably spherical.

Since the disruptor particle layer may be embedded in an epoxy/hydrogel layer, where spheres are employed as disruptor particles, due to the way spheres pack, this may lead to a barrier surface comprising a plurality of hemispherical protrusions as described below.

A number of disruptor particle layers can be present to maximise pressure impulse mitigation. It is preferable, for example, if 3 to 10 layers are utilised, e.g. 3 to 5 layers. Again, where spheres are used as the disruptor particles, these will pack to form a hexagonal layered structure as is well known.

It is a particular object of the invention to ensure that the disruptor particles are aligned or regularly packed and then autoclaved. The resulting structure would be a relatively lightweight armour. This forms a further aspect of the invention. It is envisaged that when the disruptor particles are all of the same size these can be packed very tightly in a type of face centred cubic arrangement. These can be held in place using an adhesive or hydrogel and then the whole ensemble can be compressed. The resulting material is very hard and will be very difficult for a penetrator to penetrate. On hitting the tightly packed disruptor particles it is envisaged that the penetrator will deflect and spin and thus rapidly lose energy.

Viewed from another aspect the invention provides a process for preparing an armour comprising arranging disruptor particles in a plurality of layers in a face centred cubic arrangement in an adhesive or hydrogel; and

compressing the disruptor particles.

The use of disruptor particles in the barrier of the invention has many advantages. Firstly, when the barrier absorbs an impact, the disruptor particles crush to a powder rather than splinter. Conventional armour materials are known to splinter under high impact. Whilst the bullet may therefore be stopped, damage to personnel can still occur through splintering of the pressure mitigating material. The use of ceramic balls minimises this hazard since no splintering occurs.

Moreover, the powdered ceramic disruptor particle is held within the embedding matrix.

Also, by using a plurality of small disruptor particles as opposed to a continuous layer of material, e.g. a ceramic tile, the barrier remains stronger after initial impact. When using a solid continuous layer in conjunction with a water gel, e.g. a ceramic tile as opposed to ceramic spheres, a larger portion of the barrier may be weakened after a first impact. The pressure impulse of the first impact is believed to be transmitted throughout a portion (e.g. a circle of diameter radius 10 cm) of the continuous barrier weakening therefore a large portion of it. This effect is also observed when a plurality of tiles are used. Thus, a fracture caused by an impact can be transferred from tile to tile extending the area of damage in the barrier and hence weakness significantly beyond the initial impact point.

For disruptor particle based layers, the damage is very localised meaning that the rest of the barrier remains integral and capable of absorbing further impacts. For this reason it is envisaged that positioning the disruptor layer before the tile layer may be advantageous.

It is also been found that the disruptor particles deflect a projectile and therefore act to blunt, break or otherwise redirect the tip of a ballistic penetrator.

The overall thickness of the disruptor particle layer may be 2 to 20 mm in thickness, preferably 3 to 10 mm in thickness. It will be appreciated that thicker layers tends to mean stronger panels but extra weight. The idea here is to maximise strength whilst minimising weight. The dimensions above are a compromise therefore between strength and weight.

Adhesive

It is preferred if the disruptor particle layer is set in an adhesive such as an epoxy resin. The armour panel of the invention preferably comprises an epoxy resin layer. Epoxy resins are thermosetting polymers formed from reaction of an epoxide resin with a polyamine hardener and are widely commercially available. The disruptor particles discussed below are preferably embedded in this resin.

Epoxy resins are therefore copolymers. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The hardener consists of polyamine monomers, for example triethylenetetramine (TETA). When these compounds are mixed together, the amine groups react with the epoxide groups to form a covalent bond. Each NH group can react with an epoxide group, so that the resulting polymer is heavily crosslinked, and is thus rigid and strong.

The process of polymerization is called curing, and can be controlled through temperature, choice of resin and hardener compounds, and the ratio of said compounds.

Any suitable epoxy resin can be used in the invention.

Hydrogel

As an alternative to epoxy resins, it is possible in some embodiments of the invention to use a hydrogel rather than an epoxy resin. Hydrogels of use in this aspect are preferably those described in W02006/125969 and are preferably based on crosslinked gelatin hydrogels. The layer is therefore formed by a crosslinked blend of water and gelatin. Typically there will be 10 to 45 wt % gelatine in that blend. A multifunctional cross-linking agent can be used to cross-link the material. Any epoxy resin layer or hydrogel layer is preferably of the same thickness as the disruptor particle layer as the particles are preferably embedded within the resin or hydrogel.

The combination therefore of the resin/hydrogel and the disruptor particle layers gives rise to a layer of 2 to 20 mm in thickness, preferably 3 to 10 mm in thickness.

Backing Layer

It is also preferred if the armour panels of the invention comprise a backing layer. This can simply be a support layer which can carry the disruptor particle and adhesive layer. Ideally however, the backing layer also adds to the strength of the armour. It is important that the backing layer and the disruptor layer adhere strongly together. This prevents delamination of the armour when it is struck by a projectile. It may therefore by that the backing layer is functionalised to carry reactive groups that can interact favourably with the hydrogel of the disruptor layer or with the adhesive.

The backing layer preferably refers to a cross-ply of multiple layers of a material which is then itself compressed under heat and pressure in an autoclave to form a very hard, very thin backing layer. There can be 40 to 100 individual sheets in a backing layer.

The backing layer can be formed from any convenient material but is typically a polymer fibre composite. Such a composite might be formed from aramid fibre, carbon fibre, nylon, fibreglass or a polyolefin.

The backing layer is preferably an ultra-high-molecular-weight polyethylene layer (UHMWPE). The weight average Mw of these polymers will typically be in excess of 1 million (measured by intrinsic viscosity) usually between 2 and 6 million.

These polymers are available commercially from suppliers such as Dyneema.

The backing layer may be 2 to 20 mm in thickness, preferably 3 to 10 mm in thickness.

It is possible for the composite armour of the invention to comprise a mixture of two or more backing layers, such as an aramid layer and a UHMWPE layer.

In some embodiments, it is preferred to provide a synthetic fibre layer such as a Kevlar type layer (i.e. a layer of formula (—CO—C₆H₄—CO—NH—C₆H₄—NH—)_(n)) between the ceramic layers and any UHMWPE layer.

The use of an UHMWPE and an additional synthetic fibre layer enhances the ballistic ability of the panel and also prevents delamination. A major problem with composite armour is the delamination of the layers within the armour when the panel is struck by a penetrator. The skilled man is looking therefore to maximise panel strength by preventing delamination.

The use of a synthetic fibre such as Kevlar adjacent the ceramic material may enhance laminate strength.

It may be necessary to treat the backing layer or a synthetic fibre layer to enhance interaction between the layers in the composite armour.

For example, the treatment of the synthetic fibre layer with an amino silane is possible. Alternatively, an adhesive layer might be used to adhere the backing layer to the armour panel.

Layer Order

It is preferred if the backing layer is used as a backing layer on the composite armour of the invention. It should therefore form the most inner layer.

The ceramic tile layer preferably contacts the disruptor particle embedded epoxy resin or hydrogel resin layer. Either layer can be outer or inner although it is preferred if the ceramic tile layer is outer.

The backing layer may be in contact with the inner of the ceramic tile or disruptor particle layer although other layers may also be present. It is preferred if the backing layer contacts the disruptor particle/adhesive/hydrogel layer.

Other Features

The pressure impulse mitigating barrier of the invention may comprise an array of protrusions, e.g. hemispherical protrusions, formed, for example, from the epoxy gel. The barrier may therefore have a structure akin to bubble wrap. In the present invention however, the protrusions are solid. By solid therefore is meant that the protrusions are not gas or liquid filled.

The protrusions need not be hemispherical (although this is preferred), any suitable shape is employable, e.g. rectangular, hexagonal or triangular protrusions or mixtures of differently shaped protrusions. The person skilled in the art will appreciate that a protrusion need not be a perfect hemisphere, square etc. Hemispheres may be more hemi-ovoid in shape, be carapace shaped or may become flattened slightly so as to form a more cylindrical or conical shapes. These will all fall within the scope of the term hemisphere however.

The protrusions can be present on both sides of the armour panel but are preferably present on one side of the panel only. This allows a flat side to present which can be adhered to a substrate. It is possible therefore to adhere two single sided pressure mitigating barriers to either side of a supporting substrate, e.g. a fibreglass layer or ceramic tile, to form a barrier in which protrusions are present on both sides of a supporting substrate.

The protrusions are preferably arranged in a regular array, i.e. the pattern of the protrusions repeats in some fashion. Typically therefore the pattern may involve straight lines of protrusions or preferably a hexagonal array. Ideally therefore, the barrier comprises a regular two-dimensional array of protrusions. In particular, where the protrusions are hemispherical, they pack in a hexagonal geometry.

The dimensions of the protrusions can vary over broad limits but they may be of the order of 0.1 cm to 10 cm, e.g. 0.5 to 7.5 cm, preferably 0.75 to 5 cm, about 1 cm at their broadest diameter (e.g. diagonally for a square or rectangular protrusions). The protrusions might be 0.1 to 25 mm in maximum height, e.g. 0.5 to 10 mm. It will be possible to use a mixture of differently sized protrusions, different patterns and/or differently shaped protrusions although it will be appreciated that making all the protrusions identical in the same pattern makes manufacture easier and is therefore preferred.

Panels

The armour panels of the invention can be made as thick or thin as desired. Ideally, they are as thin as possible whilst having the necessary ballistic resistance. The panels may be 10 to 2000 mm such as 10 to 100 mm, e.g. 10 to 50 mm in thickness. It will also be possible to vary the thickness of the sheet along its length so that thicker areas are present in areas where particular protection is needed. The other dimensions of the armour panels will be dictated by the nature of the entity which is being protected by the panel.

There is also an optimum size for each panel. Having a plurality of smaller panels enhances performance by preventing cracking propagation through a whole panel. Ceramic tiles can crack when struck by a penetrator and having a series of smaller panels reduces the instance of such propagation. Dimensions may be up to 1 m by lm, such as no more than 0.75 m to 0.75 m, preferably in the range 100 cm to 700 cm.

The armour panel is preferably planar but can be made curved if necessary. It may prove advantageous for example, to use a concave or convex barrier or one which is waved. Such curved barriers may be essential when fitting the barrier on curved surfaces.

It is possible to position the ceramic tile layer outside or inside (relative to the incoming penetrator) the disruptor particle layer. The disruptor particle layer works particularly well when positioned behind the ceramic tile. This is possibly because the ceramic tile first reduces the energy of the penetrator before the disruptor particle layer deflects it. The spinning penetrator cannot then rip through the essentially continuous backing layer.

Ceramic systems usually perform poorly because cracks propagate quickly through ceramics. Our system can tolerate multiple hits. We believe this is due to size of tiles, (many small vs few large) our material and the way we use it, or possibly the effect of balls. All of this reduces crack propagation.

Any panel of this invention may additionally comprise other layers not mentioned above, for example, a fibreglass layer, or a dilatant layer (e.g. polyethylene glycol layer). A fibreglass layer is especially useful as a front layer on the panel. Moreover, it is within the scope of the invention to overlap layers to maximise strength.

A dilatant is a material which thickens upon applied shear stress, e.g. may turn solid upon applied shear stress and examples thereof are polyethylene glycols and silicones.

The thickness of additional layers can of course vary depending on the nature of the material involved. Suitable thicknesses range from 1 to 100 mm.

Gaps

It is a particular feature of the invention that multiple armour panels can be used, separated by a gap. Typically this gap will simply be an air gap but it could also be filled with a filler material such as one which essentially offers no weight contribution to the armour. Such a material might be a foamed material, polystyrene and the like. These materials therefore offer little in terms of ballistic resistance but little in terms of weight. It is preferred, however, if an air gap is used. By leaving a gap between panels, it has been found that panels perform better, arguably synergistically. Each panel can be as defined above and can be the same or different. Thus, a panel /gap/panel arrangement can be employed. The term air gap is used here as the gap between panels is almost certain to be filled by air. It is in theory possible to seal the top and bottom of the gap and fill the space with some other gas and the term air gap is intended to cover that option although ideally, the gap will comprise air.

The size of the gap may vary but is typically 8 to 300 mm, preferably 15 to 200 mm in width, more preferably 20 to 150 mm. Larger air gaps can of course be used, e.g. up to 2 m, such as up to 1.5 m, preferably up to 1.0 m, ideally up to 0.5 m. It will of course be possible to use multiple panels and multiple gaps such as panel gap panel gap panel and so on. Gaps need not be the same size. Panels need not be the same. In a three panel, two air gap system, it may be preferred if the first air gap is smaller than the second air gap.

The use of an air gap with two panels of the invention is synergistic as the two panels with air gap perform better than two panels which are in contact with each other.

All layers of the pressure impulse mitigating barrier can be carried in a suitable container if required such as a metal frame, or polymer frame such as a polypropylene frame.

Manufacture

The disruptor particle layer can be easily constructed by placing those particles in a suitable mould and allowing then to pack naturally. An epoxy resin or hydrogel can then be allowed to set around that layer.

This disruptor particle layer is preferably brought into contact with the ceramic tile layer. It is preferred therefore if these layers are in contact with each other, irrespective of which is outer and inner.

The backing layer is constructed separately and simply placed on the back of the panel.

In order to maximise the strength of the panels of the invention, it is preferred if once the layers are in place, the whole ensemble is compressed and optionally heated. Heating can be effected in a high temperature autoclave for example at a temperature of 60-150° C.

Suitable compression pressures are 2 to 20 megapascals

The overall panel of the invention can be 10 to 100 mm in thickness, preferably 15 to 40 mm in thickness.

Applications

The panels of the invention could have important applications in the military and for the general public close to industrial sites such as chemical storage facilities, nuclear reactors or research laboratories or areas where transportation of hazardous materials occurs. The panels could be used in body armour as well as vehicle armour for instance.

The panels of the invention can be formed into any suitable shape depending on the nature of the protective barrier desired. The width of the material will depend on the nature of the use.

When used as a protective layer over building cladding, it is important that the lower part of the building is protected from the effects of a blast. Thus, the protective water gel barrier may be adhered only to the lower part of a building, e.g. the bottom seven floors since this is the area which suffers from the greatest blast impact from a ground based explosion. Some buildings might require complete protection, e.g. nuclear power stations, where protection from missiles and the like might be important.

The protective barrier may be continued inside the building on partitions or inside walls to strengthen the structural resistance to blast. The material may also be used as a protective surface across the whole facade of a building to protect against explosive pressures from very large explosions or from air-borne contaminants from an explosion.

Barriers may also be formulated as protective blankets, or clothing for personnel or as tent coverings or coverings for temporary buildings. Thus, the barrier could be in a form to protect the eyes, ears or feet, e.g. as shoes.

The barriers are of particular use in the disruption of the flight of projectiles, i.e. can act as armour by protecting against bullets etc.

Projectiles may be in the form of bullets or rockets travelling at speeds that may be up to 1000 metres/second. The invention is ideally suited to stopping projectiles with a calibre of 50 mm or less.

Thus, the barriers of the invention have a range of applications from bullet proof vests and helmets to replacement for sandbags to protect army personnel from enemy fire. Most importantly, the armour may be used as vehicle armour. Vehicles to be armoured are typically land rover type vehicles which may only need armour in combat whereas outside of combat they may be unarmoured.

Removable Panels

In this regard, a particular aspect of the invention is the use of panels of the invention as removable armour. When a vehicle is travelling in a reduced threat environment, the weight of armour on that vehicle is a hindrance. It slows the vehicle down and makes turning corners more hazardous as the vehicles are invariable unbalanced when carrying thick armour. This makes them prone to rolling over on a fast turn.

When the vehicle enters an area of insurgent or enemy activity, the vehicle needs to be armoured however. It is envisaged that the panels of the invention can be designed to slot into a suitable carrier mechanism on a vehicle so that the vehicle can be up armoured when required and down armoured once a threat has passed. Armour panels can be stored in a convenient facility and placed upon vehicles only when necessary.

This forms a still yet further aspect of the invention. Thus viewed from another aspect the invention provides a vehicle comprising attachment means to allow attachment and detachment of at least one armour panel as hereinbefore defined to said vehicle, wherein said vehicle is adapted to carry an armour panel as hereinbefore defined in combat and wherein said armour panel is removable from said vehicle when said vehicle is no longer in combat.

Viewed from another aspect the invention provides a process for armouring a vehicle comprising removably attaching an armour panel as hereinbefore defined to said vehicle. The term removably attaching therefore means that the panels can be attached and removed again, perhaps via appropriate slots on the object.

The vehicles could be provided with a carrying mechanism that would allow two or more panels to be attached to the vehicle whilst also providing an air gap between panels as described above. This also forms as aspect of the invention.

It is envisaged that panels could simply be lowered into appropriate slots on the side of a vehicle or under a vehicle and so on. The panels should just be able to slide in and out as desired. A locking mechanism can be provided to prevent panels from falling out of position. The use of shear-proof catches may be required.

This technology would allow for replacement of damaged panels in the field thus enabling vehicles to return to action more rapidly after damage.

Panels might be tailored to meet a threat in a particular environment, perhaps with thicker or thinner panels depending on the threats a vehicle is likely to face.

It may be preferable to combine the panels of the invention with conventional slat armour to provide protection against Rocket Propelled Grenades (RPGs) and the like.

The barriers of the invention may also have utility in the protection of ships from blast or projectiles. Both commercial and military ships have been the recent targets of terrorists and military ships in particular face dangers with mines and missiles. The barriers of the invention may be used to coat either the inside and/or outside of the ship's hull to thereby act as a pressure mitigant. Where a ship has a double hull, the barrier may be used to coat both hulls or used in the cavity between hulls.

The barrier employed may be as thin as 2.5 cm and may be applied to the hull using a conventional adhesive. Thicker layers can be applied to parts of the ship where extra protection may be required, e.g. to protect parts of the hull where damage could cause the hull to split or to protect parts of the hull housing weaponry etc.

It is also envisaged that ships could be fitted with permanent or preferably temporary skirts to prevent any damage occurring to the hull at all. The skirts would take the form of vertically suspended barriers made as thin as possible to minimise weight. Such skirts may be suspended from the side of the ship, e.g. using wires, and may prevent attacks on a ship's hull from surface to surface missiles, torpedoes, mines, or terrorists in boats. In view of their weight, these skirts could be employed only on areas of the hull where explosive damage could be critical, e.g. at the centre point of the hull where explosive damage may cause the hull to split.

Also, the skirts could be employed temporarily as a ship passes through potentially dangerous waters, the skirts being removed once the ship returns to safer areas. Thus, skirts could be employed when a ship was in port, near the coastline or in a narrow channel etc but removed in open waters. The skirts create a buffer between the hull and the skirt to mitigate any explosive effects on the hull.

The barriers could also be used to protect other marine installations such as oil rigs, underwater cables, pipelines, underwater monitoring equipment and could even be used to protect submarine hulls.

The material may also have applications deep underground where tunnels could be lined with the barriers to mitigate the effects of explosions underground. Drilling equipment etc could also be protected.

Fixing the barrier to a structure can be achieved using conventional techniques. For example, for window protection, the material may be adhered to the window surface (inside and/or outside) using known adhesives such as ceramic bonds or other bonding materials that adhere to wood, concrete or glass surfaces. These materials are readily available through suppliers to dentists for bonding of ceramic veneers to teeth, and in the construction industry for bonding materials together.

It is particularly advantageous if the bond between the barrier and the window is stronger than the fixing holding the window frame into the wall. The fact that the water gel barriers are flexible ensures that they are suitable for use with many modern buildings where walls and glass are curved or unconventionally shaped.

The material could be placed in wall cavities or roof space or secured to the outside of a building by adhesives or in a frame. The person skilled in the art can devise alternative methods of fixation.

The invention will now be further described with reference to the following non-limiting examples and FIGS. 1 to 3.

EXAMPLE 1 Panel Manufacture

Panels were constructed as shown in FIG. 1. The panels were 510 mm by 510 mm in cross section and 21 mm in thickness.

All panel types were backed with Dyneema™ panels faced with a layer of Kevlar/epoxy as a bonding aid to the disruptor layer. These Dyneema panels had a total Areal Density of 8 kg/m² each. The Kevlar layer had an areal density of approximately 200 -250 gsm. The Dyneema panels were 7.9-8.1 mm thick.

There then follows two 3.3 mm layers of alumina balls set in epoxy resin (Ampreg 22 cured with a hardener) or in a crosslinked gelatin hydrogel. The resin or hydrogel forms 5-6% of the total weight of the panel.

A Morgan sintered 6.7 mm thickness silicon carbide tile (or other tile as defined later) is placed in front of the layer of alumina balls/resin and the front of the armour is covered with a 0.2 mm epoxy/fibreglass layer.

The areal density of the whole panel is 44 kg/m². This is significantly lighter than the current civilian vehicle armours (Areal Density 56 kg/m²)—designed for defeating the Dragunov 30 cal armour piercing rounds.

Armour panels according to the invention were tested with 30 mm calibre armour piercing M2 projectiles (APM2). Shots were aimed at the centre of the tiles to avoid hitting edges. FIGS. 2A and 2B shows the aim and actual hit points, respectively, on the panel. The velocity of each shot was increased until the energy of the round was sufficient to penetrate the panel. Results are presented in table 1.

TABLE 1 Ballistic Results using 30 Cal APM2 on alumina in epoxy panels Faced with Morgan 6.7 mm SiC Tiles. PP Shot APM2 Velocity Energy or Penetrator BFD of No (m/s) (kJ) CP Position Dyneema (mm) 1 852 3.9 PP Dyneema Layer 10 2 875 4.1 PP Dyneema Layer >10 3 883 4.2 PP Dyneema Layer >15 4 909 4.5 PP Dyneema Layer >20 5 938 4.8 CP Thru Witness >30 PP—Partial Penetration, CP Complete Penetration of the panel as a whole. Energy represents the total energy of the incoming round Penetrator position determines the location of the round after contact with the panel. BFD—back face deformation. This is a measure of how much the back face of the panel protrudes from its position before firing.

The V₅₀ is the speed at which a penetrator will penetrate the panel around half of the time. The measured V₅₀ for epoxy panels was 923 m/s (Energy 4.6 kJ) i.e. the average of Shots 4 & 5). The required V₅₀ for a military APM2 is 872 m/s.

TABLE 2 Ballistic Results using 30 Cal APM2 on Hydrogel Panels, Faced with Morgan 6.7 mm SiC Tiles. APM2 BFD of Velocity Energy PP or Penetrator Dyneema Shot No (m/s) (kJ) CP Position (mm) 1 910 4.5 CP Thru Witness >30 2 879 4.2 CP Thru Witness >30 3 852 3.9 PP Dyneema Layer >30 4 853 3.9 CP Thru Witness >30

The V50=853 m/s (Average of Shots 3&4). Energy 3.9 kJ

Delamination was evident between the hydrogel/alumina layer and Kevlar bonding layer.

EXAMPLE 2 Alternative Ceramic Tiles

The experiments were repeated using two different ceramic tiles, a 6 mm tile supplied by St Gobain (SG SiC hexoloy SA grade) and a 7.5 mm Australian reaction bonded SiC tile. Thinner tiles means a lower areal density. The results are presented below:

TABLE 3 St Gobain (SG SiC hexoloy SA grade) (epoxy) APM2 BFD of Velocity Energy PP or Penetrator Dyneema Shot No (m/s) (kJ) CP Position (mm) 1 906 4.4 PP Dyneema Layer 70 2 920 4.6 PP Dyneema Layer 70 3 928 4.7 PP Dyneema Layer 120 4 974 5.1 CP Thru Witness 110 5 947 4.8 CP Thru Witness >110

V₅₀=937 m/s (Average of Shots 3 & 5)

TABLE 4 7.5 mm Australian reaction bonded SiC tile (epoxy) APM2 PP BFD of Velocity Energy or Position/state Dyneema Shot No (m/s) (kJ) CP of Penetrator (mm) 1 845 3.9 PP Dyneema/tile 10 rubble 2 874 4.1 PP Dyneema/tile 50 rubble 3 912 4.5 CP Through 5 ply witness

V₅₀ Estimate 893 m/s

TABLE 5 Summary Epoxy Based Series V₅₀ Energy AD SiC facing Tile (m/s) (kJ) (kg/m2) St Gob 6 mm SiC 937 4.7 43 Morgan US 6.7 mm SiC 923 4.6 44.5 Australian 7.5 mm RBSiC 893 4.3 45

A surprising improved performance of the 6 mm Saint Gobain tile over the heavier 6.7 mm US Morgan tile was observed—a 3% improvement (Energy absorption) for a 3.5% decrease in Areal Density.

TABLE 6 Hydrogel Based Series V₅₀ Energy AD SiC facing Tile (m/s) (kJ) (kg/m2) St_Gob 6 mm SiC <756 <3.1 43 Morgan US 6.7 mm SiC 853 3.9 44.5 Australian 7.5 mm RBSiC 890 4.3 45

For the hydrogel series, the thicker tiles performed better.

TABLE 7 Shows the breakdown of areal density for two panels of the invention 7.5 mm Morgan Reaction 6.7 mm Facing Tiles Bonded SiC Sintered SiC Front Cover Areal Density kg/m2 0.38 0.33 Tile Areal Density kg/m2 23.25 21.1 of Tile Ball/gel or epoxy Areal density kg/m2 13.8 15.1 Dyneema Areal Density kg/m2 8.0 8 Totals Total mm 21.7 20.9 Thickness Total Areal kg/m² 45 44.5 Density

The epoxy panels absorbed 18% more energy than the hydrogel panel for the same Areal density.

EXAMPLE 3 Double Panels with Air Gap

Two epoxy panels or two hydrogel panels as described in example 1 or 2 (with varying SiC tile layer) were tested. Two panels were spaced 100 mm apart, i.e. employing a 100 mm air gap.

These panels were tested with 20 mm F SP's (high velocity shells) with a mass of 53.8 g backed in the cannon barrel with a brass “pusher plate” with a mass of 14.5 g.

Two energies are therefore possible. The lower assumes an impact by the FSP with the pusher plate hitting soon after. This conservative value has been used herein. The higher value assumes that both arrive connected, at the same time and act as an FSP of a combined mass of 68.3 g. This is 27% more energy than the FSP alone.

Results

TABLE 8 Shot using 20 mm FSP on Double Epoxy Panels Faced with Morgan 6.7 mm SiC Tiles. Energy Velocity Range (m/s) (KJ) Penetration Shot 1 982 26-33 CP Shot 2 953 24-31 PP

-   -   V₅₀=967 m/s (Average of Shots 1 & 2)     -   Stanag V50=960 m/s for level 4 & 5 protection.

TABLE 9 using 20 mm FSP on Double hydrogel bonded Panels Faced with Morgan 6.7 mm SiC Tiles Energy Velocity Range (m/s) (KJ) Penetration Shot 1 896 22-27 PP Shot 2 910 22-28 CP

V50=903 m/s (Average of Shots 1 & 2)

There was a single entry hole on the front panel. Evidence for a separate entry hole for the pusher plate was not found. In both cases, the close up photos of the entry holes, show highly convoluted Dyneema (white) & Kevlar (yellow) layers behind the tiles & balls.

In all cases the air gap between the panels was filled with twisted/stretched Dyneema which had breached the 100 mm gap & impacted onto the second panel. The FSP penetrated the first Dyneema layer and impacted onto the second panel. FIGS. 3A-3C show the reconstruction of the probable FSP/panel interactions until the impact with the second panel.

Note that FSP expends a large amount of energy dragging a considerable mass of Dyneema/spall (up to 1000 g) across the air gap. Momentum considerations predict that the velocity of the projectile “bundle” would hence be considerably reduced.

The rear of the second panel showed bulges & delaminations of the Dyneema layer. These were much smaller than the first panel.

The V₅₀ for the epoxy based panels was significantly higher (7%) than the hydrogel based panels.

The measured V50 for the epoxy and hydrogel panels has been summarised in Table 10.

TABLE 10 20 mm FSP V₅₀ for 6.7 mm Morgan SiC faced Double Panel VA Epoxy Hydrogel Improvement Bonded Bonded Epoxy: P7 (%) 20 mm FSP V₅₀ (m/s) 967 903 7% Energy at FSP V₅₀ (KJ) 25.2 21.9 15% Energy/Panel (KJ) 12.6 10.95 15% AP M2 V₅₀ (Single Panel) 923 853 8% (m/s) Energy at AP M2 V₅₀ 4.6 3.9 18% (Single Panel) (KJ) Ratio FSP/AP M2 V₅₀ 5.5 5.6 −3% Energies

At V₅₀, the energy absorption for the FSP was approximately 5.5 times the energy for the APM2 at V₅₀. If this relationship holds for other double panel VA's, then an increase of an APM2 V₅₀ of 10 m/s could be estimated to give an increase in the FSP V₅₀ of approximately 9 m's.

EXAMPLE 4 Triple Panels

Panels were used to construct a triple panel array with air gaps of 100 mm between the first & second panel & then 170 mm between the second & third panels. The panels used had already been used in double panel experiments and were therefore partially damaged. 50 mm calibre shots were fired.

The V₅₀ was determined as >941 m/s on testing with 2 shots. Velocities were between 878-941 m/s. Shots were placed near the edge (50 mm) of the triple panel array.

TABLE 11 50 cal APM2 V₅₀ Determinations Facing Tile, No of Panels & V₅₀ Energy AD Date Adhesive (m/s) (kJ) (kg/m2) Double, Morgan 7 mm SiC, 798 14.6 92 Epoxy Triple, Morgan 7 mm SiC, >941 >20.3 138 Epoxy, Damaged 

1. A composite armour comprising at least two armour panels, each panel independently comprising: (I) a disruptor particle layer embedded within a hydrogel or an adhesive; (II) a backing layer; said panels being separated from each other by a gap.
 2. The composite armour of claim 1 comprising at least two armour panels, each panel independently comprising: (I) a ceramic tile layer; (II) a disruptor particle layer embedded within a hydrogel or an adhesive; (III) a backing layer; said panels being separated from each other by a gap.
 3. The composite armour of claim 1 comprising: (I) a ceramic tile layer; (II) a disruptor particle layer embedded within an adhesive; and (III) a backing layer.
 4. The composite armour of claim 1 wherein said adhesive is an epoxy resin.
 5. The composite armour of claim 1 wherein said disruptor particles are ceramic spheres.
 6. The A composite armour of claim 1 wherein said backing layer is formed from ultra high Mw polyethylene.
 7. The A composite armour of claim 1 comprising said layers (I) to (Ill) in the order of (I), (II) and (III) outer to inner.
 8. The A composite armour of claim 1 wherein said armour or armour panel is 10 to 50 mm in thickness.
 9. The composite armour of claim 2 wherein said gap is an air gap.
 10. (canceled)
 11. An entity selected from the group consisting of a vehicle, helmet or body armour comprising the composite armour of claim
 1. 12. An object adapted to carry a composite armour comprising: (I) a disruptor particle layer embedded within a hydrogel or an adhesive; (II) a backing layer; wherein said composite armour is removably attached to the object.
 13. A vehicle comprising an attachment means to allow attachment and detachment of at least one armour panel of claim 1 to said vehicle, wherein said vehicle is adapted to carry said composite armour panel in combat and wherein said armour panel is removable from said vehicle when said vehicle is no longer in combat.
 14. A process for armouring a vehicle comprising removably attaching an armour panel of claim 1 to said vehicle.
 15. A process for preparing an armour comprising arranging disruptor particles in a plurality of layers in a face centered cubic arrangement in an adhesive or hydrogel; and compressing the disruptor particles.
 16. The composite armour of claim 1 wherein said panels are separated by a gap having a thickness of 5 mm to 200 mm.
 17. The composite armour of claim 16 wherein said gap is an air gap.
 18. The object of claim 12, wherein the object is a vehicle. 